The hazards of occupational exposure to radon daughters relative to environmental exposure is significant both for occupational and environmental health. Much attention has been paid to relative physical factors (bronchial epithelial dose /WLM) in the two situations, but almost no attention to the relative biological factors (risk/unit bronchial dose in miners vs general public). These biological differences arise because of the (average) thicker mucosal layers in the 70% of miners who smoke, compared to the approximately 70% of the general public who do not smoke. Preliminary calculations for a single biological endpoint suggest that this biological factor may differ by about a factor of two between miners and the general public, which would be larger than any physical differences in dose per unit WLM exposure. The aim of this small-grant pilot study is to produce evaluations of the relative biological hazards of radon daughters per unit lung dose, for pertinent biological endpoints, for miners vs. environmentally-exposed home residents. In particular, it is proposed to 1) analyze previously-collected biological data to quantify how the relative biological hazard varies with LET (Linear Energy Transfer, or stopping power, dE/dx) and its microdosimetric correlate, lineal energy. only biological measurements pertinent to risk estimation, namely oncogenic transformation, mutation, and chromosomal damage, will be considered; 2) use Monte-Carlo simulation of alpha-particle transport, together with the best available data on mucosal and epithelial thicknesses in smokers and non smokers, to estimate the energy deposition characteristics of the radon-daughter alpha particles, in the cells at risk in the bronchial epithelia of miners and the general public; 3) combine the data from (1) and (2) to obtain relative biological risk factors for occupational miners and the general public.